0.21.0 release

[songy23]

A placeholder for the next minor release. Remaining items (feel free to edit or add more):

• Finish up the implementation for Cumulative APIs (Metrics: Implementation of Cumulative APIs. #1856).
• Decide whether to drop event when disrupter queue is full (Prevent blocking on queue overflow (#1809) #1837).
• Investigate the issue with Stackdriver exporter (Stackdriver metric units missing #1841).

/cc @paivagustavo

[paivagustavo]

Seems like #1837 is going to take longer than expected because it must be discussed on the opencensus-specs. Can this be delayed to next release? It would help me a lot if the new changes on master get released.

[bogdandrutu]

I would suggest that we skip, but with the idea to do a new release sooner that will include that change to not block people that need the non-blocking.

[songy23]

SGTM, we'll hold #1837 till next release (which waits on the conclusion of census-instrumentation/opencensus-specs#262). Will do a release without that change first.

[songy23]

Release is done: https://github.com/census-instrumentation/opencensus-java/releases/tag/v0.21.0.